Ball-seat apparatus and method

ABSTRACT

An apparatus for restricting fluid flow includes: a ball receiving element disposed in a fluid conduit and configured to receive a ball that has been advanced through the fluid conduit and at least partially restrict fluid flow, the fluid conduit having a longitudinal axis; and at least one feature disposed at the fluid conduit and configured to at least one of reduce a rate of deceleration of the ball due to actuation of the apparatus and reduce pressure waves generated by an impact between the ball and the ball receiving element.

BACKGROUND

In the drilling and completion industry and for example in hydrocarbonexploration and recovery operations, a variety of components and toolsare lowered into a borehole for various operations such as productionoperations, for example. Some downhole tools utilize ball-seatassemblies to act as a valve or actuator. Ball-seat assemblies are usedwith, for example, hydraulic disconnects, circulating subs andinflatable packers.

Actuation of a ball-seat assembly generally includes releasing a ball orother plug into a fluid conduit and allowing the ball to drop or bepumped onto the ball seat and restrict fluid flow therein. The impactbetween the ball and the ball seat can produce pressure waves, which cancause wear and/or damage to components of the assembly, vibrations andtubing failure. For example, fluid in downhole applications can bepumped at rates of up to about 80 bbl/min, which can cause an enormouspressure surge upon impact of a plug or ball on a seat, which causeswear and potential damage to downhole components.

SUMMARY

An apparatus for restricting fluid flow includes: a ball receivingelement disposed in a fluid conduit and configured to receive a ballthat has been advanced through the fluid conduit and at least partiallyrestrict fluid flow, the fluid conduit having a longitudinal axis; andat least one feature disposed at the fluid conduit and configured to atleast one of reduce a rate of deceleration of the ball due to actuationof the apparatus and reduce pressure waves generated by an impactbetween the ball and the ball receiving element.

A method of restricting fluid flow includes: releasing a ball into afluid conduit and receiving the ball in a ball receiving elementdisposed at the fluid conduit and at least partially restricting fluidflow, the fluid conduit having a longitudinal axis; and at least one ofreducing a rate of deceleration of the ball due to actuation of theapparatus and reducing pressure waves generated by an impact between theball and the ball receiving element by at least one feature disposed atthe fluid conduit.

BRIEF DESCRIPTION OF THE DRAWINGS

The following descriptions should not be considered limiting in any way.With reference to the accompanying drawings, like elements are numberedalike:

FIG. 1 is a cross-sectional view of an embodiment of a ball-seatassembly;

FIG. 2 is a partial cross-sectional view of an embodiment of theball-seat assembly of FIG. 1;

FIG. 3 is a perspective view of another embodiment of the ball-seatassembly of FIG. 1; and

FIG. 4 is a flow diagram depicting a method of restricting fluid flow ina conduit.

DETAILED DESCRIPTION

The apparatuses, systems and methods described herein provide for thereduction of a ball-seat impact and the mitigation of pressure wavescaused by actuation of a ball-seat assembly. A ball seat assemblyincludes a ball receiving element such as a ball seat. The ball seatincludes a plurality of axially offset ball seat assemblies or seatingcomponents disposed at a fluid conduit and protruding at least partiallyinto the fluid conduit. In one embodiment, each seating component has across-sectional shape that is contoured to create one or more fluidpassageways when a ball contacts the seating component. The contouredseating components may be circumferentially offset so that a portion ofthe fluid in the conduit flows through the ball seat as the ballcontacts each seating component. In one embodiment, one or more of theseating components is axially contoured and/or compliant to reduce theimpact of the ball on each component and control the reduction invelocity resulting from contact with each seating component. Theconfiguration of the seating components acts to incrementally slow theball as it engages the ball seat and may also incrementally reduce fluidflow as the ball is seated to reduce impact on the ball seat assemblyand reduce pressure waves resulting from the ball-seat impact.

Referring to FIG. 1, a downhole tool 10, such as a ball seat sub,configured to be disposed in a borehole 11, includes a housing 12 havinga longitudinal bore or fluid conduit 14. A ball seat assembly includes aball seat 16 included in the conduit 14 to retain a ball 18 that isreleased into the conduit 14. In one embodiment, the ball 18 is aspherical metal or plastic plug, although “ball” may refer to any typeof moveable or droppable plugging element, such as a drop plug, and maytake any desired shape or size. Actuation of the ball seat assemblyincludes releasing the ball into the fluid conduit 14, for example bydropping the ball 18 into and/or pumping the ball 18 through the fluidconduit 14 from a surface or downhole location. The ball 18 falls and/oris advanced by downhole fluid toward the ball seat 16 and is seated onthe ball seat 16 to restrict fluid flow through the conduit 14. Asdescribed herein, “axial” refers to a direction that is at leastgenerally parallel to a central longitudinal axis of the conduit 14.“Radial” refers to a direction along a line that is orthogonal to thelongitudinal axis and extends from the longitudinal axis. As describedherein, “downstream” refers to the direction of movement of the balland/or the downhole fluid, and “upstream” refers to a direction oppositethe direction of movement of the ball and/or the downhole fluid.

Referring to FIG. 2, the ball seat 16 includes a plurality of axiallyoffset seating members or seating components 22 disposed at the conduit14 and protruding radially into the conduit 14. The plurality of seatingcomponents 22 include one or more upstream seating components, such asseating component 24, axially disposed relative to a downstream seatingcomponent, such as seating component 26, to create an axial contouringthat reduces the overall deceleration of the ball 18 and brings the ball18 to a relatively gentle stop. This in turn reduces the amplitude ofpressure waves due to an incremental or fractional change in velocity ofthe ball 18. The reduction in amplitude reduces impact loading betweenthe ball 18 and the ball seat 16, which reduces pressure waves, wear onthe ball seat assembly and the potential for damage to the ball seatassembly. In one embodiment, the ball seat 16 and/or seating components22 are directly disposed on and/or attached to the inner surface of theconduit 14 or is formed from a reduced diameter portion of the conduit14. In one embodiment, the ball seat 16 is disposed on or is part of amovable component such as a sliding sleeve or other movable seat carrier20 for use, for example, as an actuator or valve.

The plurality of seating components 22 reduces the total rate ofdeceleration and increases the time rate of ball seat assembly closureduring actuation of the ball seat assembly. Seating loads can thereby bereduced as they depend on the time rate of velocity change. In oneembodiment, the ball 18 is slowed in several increments, defined by theinitial velocity of the ball 18, the resistance to movement of theseating components 22, and the axial as well as any radial offsetbetween the components. The number of increments can be represented by:

Δv=ΣΔv _(i),

where “Δv” is the total change in velocity, and “Δv_(i)” is the changein velocity for each incremental closure “i” of the flow passage. Eachclosure may correspond to one or more seating components 22 contactingthe ball 18. Since the ball impact load and the surge pressures areproportional to change in velocity, the loading occurs in thisembodiment in small increments, resulting in smaller pressure waves,instead of the total loading being applied all at once.

In one embodiment, at least one seating component 22 has across-sectional profile, i.e., a profile in a plane at least partiallyorthogonal to the longitudinal axis of the conduit 14, so that contactbetween the ball 18 and the seating component only partially stops fluidflow as the ball 18 moves downstream. In one embodiment, one or more ofthe seating components 22 has a cross sectional shape configured to formone or more conduits, or passageways upon contact with the ball 18. Thepassageways are configured to allow fluid flow therethrough when theball is in contact with a respective seating component 22. In this way,as the ball 18 contacts each seating component 22, fluid voids areformed that allow a portion of the fluid to pass through, therebydisrupting or otherwise reducing the effect of pressure waves producedduring ball-seat impact.

For example, as shown in FIG. 3, seating components 24 and 26 eachinclude a plurality of circumferentially arrayed protrusions or membersextending into the conduit 14. The separation between adjacent membersforms a fluid void formed when the ball 18 contacts each assembly.

In one embodiment, as shown in FIG. 3, the assemblies 24 and 26 arecircumferentially offset so that contact with the upstream seatingcomponent 24 forms a fluid void, and as the ball 18 advances furtheralong the ball seat 16 and contacts the downstream component 26, thefluid voids may be closed to fully cut off fluid flow through the ballseat 16. The fluid voids in each seating component 24, 26 arecircumferentially offset or otherwise arranged relative to other seatingcomponents so that in each successive contact closure the flow velocityand volume reduces fractionally rather than all at once.

In one embodiment, the ball seat 16 includes at least one additionalseating component 28 axially offset at least one of the other seatingcomponents 24, 26. Each component 24, 26 and 28 is sequentiallycontacted by the ball 18 during actuation, and the ball 18 is thusincrementally slowed until it comes to a stop and is seated. In oneembodiment, each seating component is circumferentially offset from anaxially adjacent seating component, so that the fluid voids formedbecome incrementally smaller as the ball 18 advances through the ballseat 16. In one embodiment, the ball 18 has a circumference sufficientso that the ball 18 remains in contact with each seating component 22 asit advances through the ball seat 16. In one embodiment, the seatingcomponents are circumferentially offset so that when the ball 18 comesto a rest and is seated, the ball 18 is in continuous circumferentialcontact with the seating components 22 so that fluid flow is completelycut off

Each successive seating component can be configured to control theincremental reduction in velocity of the ball 18. For example, eachseating component 22 may have a selected resistance to movement thatcauses the ball 18 to reduce its velocity by a desired amount.“Resistance to movement” may include a stiffness, compliance orelasticity of each component or constituent member, a mechanicalresistance generated by a spring or other device, or an axial shape ofthe seating component. In one example, a seating component 22 mayinclude an internal spring. In another example, a seating component 22may have a selected axial contour, such as a gradual increase in radialextension as the seating component (e.g., an elliptical shape as shownin FIGS. 1-3) extends axially downstream. The resistance to movementand/or contour may be selected so that the seating components 22 havethe same or varying resistances to movement to control the incrementalvelocity changes. The reduction of velocity may depend on thegeometrical profiles of the seating components 22 and the ball 18 (orother plugging device), the axial and angular spacing of the seatingcomponents 22, the load-deformation behavior of the contacting bodies,and/or fluid flow rates.

The seating components 22 are not limited to the embodiments describedherein, and may take any shape or configuration suitable for graduallyor incrementally slowing the ball as it engages the ball seat 16.Examples of such configurations include a ring-shaped or toroidalelastic seat disposed on an interior surface, resilient flaps, andresistant mechanisms such as spring loaded and/or articulated memberthat protrude into the conduit 14 and having a selected resistance tomovement. In other embodiments, the seating components may be formedfrom an axial contour or shape of a single seating component.

The downhole tool 10 is not limited to that described herein. Thedownhole tool 10 may include any tool, carrier or component thatincludes a ball seat assembly. The carriers described herein, such as aproduction string and a screen, are not limited to the specificembodiments disclosed herein. A “carrier” as described herein means anydevice, device component, combination of devices, media and/or memberthat may be used to convey, house, support or otherwise facilitate theuse of another device, device component, combination of devices, mediaand/or member. Exemplary non-limiting carriers include borehole stringsof the coiled tube type, of the jointed pipe type and any combination orportion thereof. Other carrier examples include casing pipes, wirelines,wireline sondes, slickline sondes, drop shots, downhole subs,bottom-hole assemblies, and drill strings. In addition, the tool 10 isnot limited to components configured for downhole use.

FIG. 4 illustrates a method 40 of restricting fluid flow in a component.The method includes, for example, actuating a valve or packer in adownhole assembly. The method 40 includes one or more stages 41-43.Although the method is described in conjunction with the tool 10 and theball seat 16, the method can be utilized in conjunction with any deviceor system (configured for downhole or surface use) that utilizes aball-seat assembly.

In the first stage 41, in one embodiment, the tool 10 is disposed at adownhole location, via for example a borehole string or wireline. In thesecond stage 42, the ball-seat assembly is actuated by releasing theball 18 into the conduit 14, for example by dropping the ball 18 intothe conduit 14 and/or pumping the ball 18 through the conduit 14. Theball 18 advances through the conduit 14 and engages the ball seat 16. Inthe third stage 43, the ball 18 is incrementally slowed by the seatingcomponents 24, 26 and/or 28. Upon contact with the most downstreamseating component (e.g., seating component 26 or 28), the ball 18 comesto a stop, and fluid flow is completely cut off or reduced by a selectedamount.

The systems and methods described herein provide various advantages overexisting processing methods and devices. The systems and methods resultin a more gradual reduction in impact velocity versus instantaneousarrest and reduces pressure waves formed by ball-seat impact. This inturn reduces damage to the ball seat assembly and improves reliability,and can enable the use of a wider range of construction materials andreduce the complexity of ball-seat design, for example by reducing theneed for relatively complex ball seat designs to reduce impact. Reducedpressure wave loading can also reduce the burst or collapse loading ondownhole tubing. Furthermore, the apparatuses described herein providean alternative lower complexity design relative to prior artapplications such as embedded springs.

While the invention has been described with reference to exemplaryembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications will be appreciated by those skilled in theart to adapt a particular instrument, situation or material to theteachings of the invention without departing from the essential scopethereof. Therefore, it is intended that the invention not be limited tothe particular embodiment disclosed as the best mode contemplated forcarrying out this invention.

1. An apparatus for restricting fluid flow, comprising: a ball receivingelement disposed in a fluid conduit and configured to receive a ballthat has been advanced through the fluid conduit and at least partiallyrestrict fluid flow, the fluid conduit having a longitudinal axis; andat least one feature disposed at the fluid conduit and configured to atleast one of reduce a rate of deceleration of the ball due to actuationof the apparatus and reduce pressure waves generated by an impactbetween the ball and the ball receiving element.
 2. The apparatus ofclaim 1, wherein the at least one feature is included in the ballreceiving element, and the at least one feature includes: at least onefirst seating component disposed at the conduit and protruding radiallyinto the conduit, the at least one first seating component configured tocontact the ball and reduce a velocity of the ball; and a second seatingcomponent protruding radially into the conduit and disposed at adownstream location relative to the first seating assembly, the secondseating assembly configured to prevent downstream movement of the ball.3. The apparatus of claim 2, wherein the at least one first seatingcomponent has a cross-sectional shape configured to form one or morefirst fluid passageways therethrough upon contact with the ball.
 4. Theapparatus of claim 3, wherein the at least one first seating componentincludes a plurality of axially successive circumferentially offsetseating components.
 5. The apparatus of claim 4, wherein respectivefluid passageways in each of the plurality of seating components areoffset from one another so that a total cross-sectional area of thefluid passageways successively decreases as the ball advances throughthe ball receiving element.
 6. The apparatus of claim 3, wherein thesecond seating component has a cross-sectional shape configured to formone or more second fluid passageways therethrough upon contact with theball, and the second fluid passageways are circumferentially offsetrelative to the one or more first fluid passageways.
 7. The apparatus ofclaim 6, wherein the ball forms a complete fluid seal with the first andsecond seating components when seated.
 8. The apparatus of claim 3,wherein the at least one first seating component includes a plurality offirst axially tapered members, each first axially tapered memberarranged circumferentially and forming a first fluid passage with anadjacent first tapered member.
 9. The apparatus of claim 8, wherein thesecond seating component includes a plurality of second axially taperedmembers circumferentially offset relative to the plurality of firstmembers, each second axially tapered member arranged circumferentiallyand forming a second fluid passage with an adjacent second taperedmember.
 10. The apparatus of claim 2, wherein each of the first andsecond seating components have an axial contour that increases graduallyin the downstream direction.
 11. The apparatus of claim 2, wherein eachof the at least one first seating component and the second seatingcomponent include at least one of a selected resistance to movement andaxial contour configured to reduce a velocity of the ball by a selectedamount upon contact with the ball.
 12. The apparatus of claim 11,wherein at least one of the resistance to movement and the axial contourof the second seating component is sufficient to stop the ball aftercontact with the first seating component.
 13. A method of restrictingfluid flow, comprising: releasing a ball into a fluid conduit andreceiving the ball in a ball receiving element disposed at the fluidconduit and at least partially restricting fluid flow, the fluid conduithaving a longitudinal axis; and at least one of reducing a rate ofdeceleration of the ball due to actuation of the apparatus and reducingpressure waves generated by an impact between the ball and the ballreceiving element by at least one feature disposed at the fluid conduit.14. The method of claim 13, wherein the at least one feature is includedin the ball receiving element, and the at least one feature includes: atleast one first seating component disposed at the conduit and protrudingradially into the conduit, the at least one first seating componentconfigured to contact the ball and reduce a velocity of the ball; and asecond seating component protruding radially into the conduit anddisposed at a downstream location relative to the first seatingcomponent, the second seating component configured to prevent downstreammovement of the ball.
 15. The method of claim 14, further comprisingreducing a velocity of the ball in successive increments by successivelycontacting the first seating component and the second seating componentby the ball as the ball engages the ball receiving element.
 16. Themethod of claim 14, wherein the at least one first seating component hasa cross-sectional shape configured to form one or more first fluidpassageways therethrough upon contact with the ball.
 17. The method ofclaim 16, further comprising reducing a fluid flow through the ball seatin successive increments by successively contacting the first seatingcomponent and the second seating component by the ball as the ballengages the ball receiving element.
 18. The method of claim 17, whereinthe ball forms a complete fluid seal with the first and second seatingcomponents when seated.
 19. The method of claim 16, wherein the at leastone first seating component includes a plurality of axially successivecircumferentially offset seating components, and respective fluidpassageways in each of the plurality of seating components are offsetfrom one another so that a total cross-sectional area of the respectivefluid passageways successively decreases as the ball advances throughthe ball receiving element.
 20. The method of claim 16, wherein thesecond seating component has a cross-sectional shape configured to formone or more second fluid passageways therethrough upon contact with theball, and the one or more second fluid passageways are circumferentiallyoffset relative to the one or more first fluid passageways.